1. Technical Field
The present invention relates to a light emitting device that uses a light emitting element, such as an organic EL (electroluminescence) element.
2. Related Art
A light emitting device, in which a plurality of light emitting elements are arranged in an effective region on a substrate and various wirings, and the like, are arranged in a peripheral region that surrounds the effective region, has been known. Each of the light emitting elements includes a light emitting layer that is formed of a light emitting material, such as an organic EL material, and that is held between a first electrode and a second electrode. In most cases, the second electrode is a common electrode that is provided commonly for the plurality of light emitting elements and is provided all over the entire effective region. However, there is a possibility that a decrease in voltage will occur along the plane of the electrode because of a resistance of the electrode itself and, then, electric potentials supplied to the light emitting elements will vary depending on a position on the substrate and, therefore, the luminance of the light emitting elements will vary depending on the position. Then, an auxiliary electrode that is formed of a material having a lower resistance than the common electrode and that is electrically connected to the common electrode has been provided in order to reduce the resistance of the common electrode (which is, for example, described in JP-A-2002-352963).
In the meantime, the auxiliary electrode is mostly formed of, for example, a light shielding member, such as aluminum. Therefore, it is desirable that the auxiliary electrode is formed to extend through a region of a gap between the adjacent light emitting elements so as not to block light that exits from the light emitting elements, and also it is desirable that the auxiliary electrode is formed using a highly accurate positioning mechanism. In contrast, the common electrode is formed of an optically transparent material and is formed uniformly in the region that covers the entire effective region. Thus, as compared with the auxiliary electrode, the tolerance of positioning is allowed to form the common electrode. Thus, the tolerance of positioning of the common electrode becomes more problematic than that of the auxiliary electrode. Thus, it is desirable that the width of the peripheral region (so-called “window frame region”) is sufficiently ensured on the substrate so that the tolerance of the common electrode may be absorbed. This as been an obstacle to a reduction in size of the device.
In addition, circuit elements, such as transistors, to control emission of light of the light emitting elements are arranged in a lower layer under the common electrode and the auxiliary electrode. For this reason, an insulating layer is provided between the circuit elements and both the common electrode and the auxiliary electrode, so that the common electrode and the auxiliary electrode are insulated from the circuit elements. However, when the insulating layer has a step, there is a possibility that the electrode positioned at an upper layer portion that overlaps the step may break or crack. Because the resistance value of the electrode that has broken or cracked increases, the light emitting elements will have a remarkable luminance non-uniformity.